As a process of producing of HFC-245fa, a process is known in which 1,1,1,3,3-pentachloropropane is fluorinated with hydrogen fluoride (hereinafter, also referred to as HF) in the presence of several catalysts in either vapor phase or liquid phase.
In such a process to obtain HFC-245fa, it is necessary to recover HFC-245fa by removing HF from the product since unreacted HF generally remains in the reaction product in addition to HFC-245fa. In such case, HF is simultaneously required to be recovered and recycled to the reaction system from the economical viewpoint. However, HFC-245fa is found to form an azeotropic mixture with HF, which was disclosed in, for example, Japanese Patent Application No. 9085/1997 and Japanese Patent Kokai Application No. 156701/1997 both filed by us. We also found that it is difficult to recover HFC-245fa substantially free of HF through a simple distillation since the composition of such azeotropic mixture varies depending on the pressure, for example, the azeotropic mixture contains 55% by mole of HF at a pressure of 5 atm. In addition, it is not commercially easy to recover HFC-245fa solely without recovering such a large amount of HF.
As processes for separating fluorohydrocarbon compounds from HF, several processes, for example, a process to let each component of the mixture separate from each other to form two liquid layers and recover each component by distillation (Japanese Patent Kokai Publication No. 167803/1990); a process to use sulfuric acid as an extraction agent for HF (U.S. Pat. No. 3,873,629) and a process to remove HF through absorption into hydrofluoric acid (also referred to an aqueous HF solution) (Japanese Patent Kokai Publication No. 279277/1993) are known. Further, it is also known to successively distillate the mixture with two distillation columns in which the internal pressures are different each other, using a property that the composition of the azeotropic mixture varies depending on the pressure as disclosed in Japanese Patent Kokai Publication No. 178768/1993.